Photoresists, and in particular those formulated for 193 nm lithography, tend to have very low unexposed dissolution rates. Unlike deep ultraviolet (DUV) photoresist polymers for use at 248 nm exposure wavelengths that are primarily based on the base-soluble 4-hydroxystyrene monomer (HSM) derived unit which permits dissolution of the polymer in alkaline developer, 193 nm photoresist polymers cannot incorporate the most common aromatic monomers such as HSM which has a high absorbance at 193 nm. Instead, monomeric units incorporating other base soluble groups, or those aromatic monomers having a relatively low absorbance at 193 nm, have been used, such as the less absorbing 2-hydroxy-6-vinyl-naphthalene or monomers incorporating a hexafluoroalcohol (HFA) unit. To date however, photoresists incorporating polymers based on these base-soluble groups can exhibit poor line width roughness (LWR). In addition, in the case of HFA-based monomers, polymers incorporating these groups have undesirably reduced etch resistance due to the presence of fluorine, relative to non-fluorinated monomers such as HSM.
Other functional groups with base solubility and high transparency have been described, such as those found in Japanese Patent Nos. JP 63-127237, JP 1998-060056, and JP 1999-1065953, and in European Patent No. EP 0 875 496 A1. However, there remains a need for photoresist polymers for 193 nm, which exhibit improved LWR and etch control.